1. Field of the Invention
The present invention relates to a document reader comprising a platen for an original document to be placed thereon and a hold-down member capable of opening and closing relative to the platen, and to an image forming apparatus provided with the document reader.
2. Description of the Related Art
Document readers of the type for reading a document made stationary, in general, read image information from an original document placed stationarily on a platen glass by moving a document scanning optical unit positioned below the platen glass for reading the original document.
Such a document reader is provided with a hold-down member for fixing an original document into intimate contact with the platen glass in order to read image information from the original document. Usually, the hold-down member is pivotally mounted on the document reader body so as to be openable and closable relative to the platen glass.
In reading an original document with such a document reader, the user first opens the platen glass, places the original document on the platen glass, and then closes the hold-down member to fix the original document on the platen glass into intimate contact with the platen glass. By so doing, the original document is set stationary on the platen glass at a predetermined position as pressed against the platen glass, whereby the document reader is allowed to read image information from the original document under favorable conditions.
Such hold-down members generally have substantially the same size as a maximum-size document that can be wholly read at a time by the document reader and are frequently large-sized as large as A1 size, A0 size or the like.
With such a large-sized hold-down member opening and closing, an original document placed on the platen glass is sometimes moved off its right placement position due to wind pressure generated by the opening and closing of the hold-down member moving or by a like cause.
That is, such wind pressure makes it difficult to place the original document at its proper position on the platen glass and, hence, it is possible that the image of the original document is read as moved off its right position or partially lacking.
Such a document reader may be provided on a composite apparatus having multiple functions such as a copying machine or a printer. In this case the image reader is disposed in an upper portion of the composite apparatus.
For this reason, if the composite apparatus is provided with plural sheet feeding cassettes in tiers, the level at which the hold-down member is disposed becomes undesirably high, which might make it difficult for the user to open and close the hold-down member.
In an attempt to overcome this inconvenience, a prior-art document reader, as disclosed in Japan Patent Laid Open Hei No. 7-72555 for example, has a hold-down member provided with grips on a front side and opposite lateral sides thereof for allowing the user to open and close the hold-down member from any one of these three sides.
Further, each of the grips in the document reader disclosed in the aforementioned publication is slidable to a position at which the user can manipulate the grip easily. Thus, the grips allow the user to open and close the hold-down member from any direction with respect to the document reader thereby imparting the document reader with improved open/close operability.
The prior-art document reader, however, involves the problem that the hold-down member has increased size and weight because of the provision of the plural grips rendered slidable. Such increased size and weight lower the convenience in opening and closing the hold-down member and might make it difficult for children and handicapped persons in particular to open and close the hold-down member smoothly.
As described above, the hold-down member of the aforementioned document reader has substantially the same size as a maximum-size document that can be wholly read at a time by the document reader. For this reason, the whole hold-down member has to be opened and closed whenever the document reader is to read an original document, regardless of the size of the document. Therefore, the increase in the size and weight of the hold-down member constitutes an important factor that deteriorates the open/close operability of the hold-down member.
Accordingly, it is an object of the present invention to provide a document reader which is capable of properly adjusting the operability of its hold-down member in accordance with the size of an original document to read thereby effectively preventing the original document from moving off its right position.
If such a document reader is capable of recognizing the size of the original document upon placement of the original document, a region of the original document that should be subjected to reading can be determined before the reading of the original document without the need to prescan the original document and, therefore, an improved reading efficiency can be expected.
Another object of the present invention is to provide an image forming apparatus provided with such a document reader.